This invention relates generally to solenoid actuated valves and more specifically to an improvement in a mechanical override for a solenoid actuated hydraulic valve.
Solenoid actuated hydraulic valves are used in many types of machines to control the flow of fluid power to and from hydraulic power devices such as hydraulic cylinders or hydraulic motors. The valves are controlled by circuits which selectively energize the various solenoids in accordance with the intended operating sequence for the various parts of a machine. Thus, for proper machine operation it is intended that the solenoid valves always be under the control of the associated control circuits, and unauthorized tampering with the valves is not intended. In other words when a machine is in productive use, its valves should not be susceptible to unauthorized tampering, and hence from this standpoint any features which render a valve more prone to tampering than it might otherwise be are, as a general rule, to be avoided if possible. Yet from other standpoints, the incorporation of certain features such as mechanical overrides are demanded even if they render a valve more prone to tampering.
Mechanical overrides (often called manual overrides) are incorporated in certain existing solenoid actuated hydraulic valves to override the operation of the solenoids. Mechanical overrides are for the principal benefit of certain machine builders to facilitate assembly, adjustment, trouble shooting, and check-out of machines by their personnel. Once a given machine has been tuned to proper operation by the builder, the mechanical overrides have served their principal purpose. After a machine has been accepted by a customer, the elimination of mechanical overrides will render the machine less prone to unauthorized tampering.
Thus, the manufacturer of hydraulic valves is confronted with a dilemma. In order to offer products acceptable to certain machine builders, the incorporation of mechanical overrides into solenoid operated valves is virtually essential. On the other hand, a customer who purchases a machine from one of these builders may deem the presence of mechanical overrides objectionable. He is left with really only a limited number of choices. For one, he may begrudgingly accept the mechanical overrides and run the risk of unauthorized tampering; or he must incur the extra expense of taking measures to restrict access to the valves. An unfortunate drawback in restricting access to the valves is that it can hinder legitimate access by skilled maintainence personnel in times of need.
Because certain machine builders want mechanical overrides to facilitate their own manufacturing and check-out procedures, their position invariably prevails. Those machine tool builders leave it to their customers to take adequate precautions against unauthorized tampering with the mechanical overrides. As a practical matter, control of unauthorized tampering with mechanical overrides is not 100% foolproof even though reasonable safeguards may be taken.
One possible solution to this problem would be to replace all mechanical override types of solenoid valves on a machine before it is put to use by a customer. Where a machine contains a vast number of such valves, this would impose a significant delay in putting the machine into productive use, not to mention the extra cost of having to replace the valves.
Therefore, this whole situation has been one which has been tolerated over the years, even though it is not a desirable one.
The present invention is directed to a new and improved mechanical override for a solenoid operated control valve which provides a particularly convenient solution to this problem and which can be relatively expeditiously accomplished and with must less expense than would be involved in replacing complete valve assemblies. The requirements of machine builders can be accommodated since a valve embodying principles of the present invention will comprise a mechanical override feature, yet the desires of users of the machines can also be met since the mechanical overrides are in the form of cartridges which can be quickly removed from valves and replaced by plugs to eliminate the manual override functions from the valves.
A further attribute of the invention is that because of its replaceable cartridge nature, it can accomodate standard valve bodies and valve configurations. In other words, extensive re-tooling of existing valve models is not required.
The improvement of the invention appears from casual observation to be relatively simple, yet its simplicity belies the myriad of specific features which are embodied in its construction and the attributes which it possesses. Some of these attributes are specific to the particular embodiment of valve involved but others have generic application. In the disclosed preferred embodiment of the present invention, the mechanical override cartridge separably mounts on a solenoid tube. The cartridge comprises a main tubular body which removably mounts on the solenoid tube via a screw thread connection. The mechanical override forms a closure for, but is axially shiftable within, the bore of the main cartridge body. Thus, when a solenoid actuated valve is manufactured for a machine builder who demands mechanical override features, the valve is manufactured with the mechanical override cartridge mounted on the solenoid tube. This allows the valve to be solenoid operated in the usual manner by electrical control circuits, yet it affords the machine tool builder the capability of conveniently mechanically overriding the solenoid's operation. The mechanical override can be manually operated by authorized personnel through use of a suitable tool.
When the machine builder has completed a machine and it is ready for use by a customer, the mechanical override cartridges can be conveniently removed by unscrewing them from the solenoid tubes and replacing them by threaded caps.
The invention yields several important advantages when used in association with a solenoid tube. The tube is provided with an aperture for the replaceable mounting of the mechanical override cartridge. This allows the tube to be fabricated without the cartridge being present, and it provides access for flushing the tube's interior with the cartridge removed. These are important attributes which are not present in existing solenoid tubes of the same geneal type. Such an existing tube has the override disposed in a bore in the tailpiece with an elastomeric O-ring providing a circumferential seal between the wall of the tailpiece bore and the outside of the override. The tailpiece is disposed at, and joins with, one end of a tubular sleeve. The armature is disposed within the sleeve, and the opposite end of the sleeve is closed by the pole piece. With such a construction, the overrides are non-removable, and non-destructive access to the tube's interior is not attainable.
Moreover, the fabrication procedure for such tubes requires use of certain joining techniques because of the non-magnetic nature of the sleeve. These techniques involve a critical quenching which, if not properly carried out, can result in heat propagating into the tailpiece to damage the seal between the override and the wall of the tailpiece bore. This problem is commonly referred to as O-ring burn and can cause damage to, or even total destruction of, the seal. Joining procedures, even sophisticated ones, may also result in the introduction of foreign matter, such as flash, into the tube's interior. Because existing tubes have non-removable overrides and are essentially enclosed, foreign matter cannot be flushed out nor can a damaged O-ring seal be replaced. Thus, a defective tube must be scrapped, and in actual practice, the production yield is noticeably less than 100%. With the present invention a significant improvement in yield, and attendant savings can result because the tube's interior can be flushed via the mounting aperture for the override cartridge and because the possibility of O-ring burn is eliminated.
An advantage of the invention which has generic application apart from solenoid tube mounting for the override cartridge involves the significant alleviation, or even entire elimination, of bore scoring which may occur within the bore containing the mechanical override. Conventional mechanical overrides are often operated by any convenient means which may be available, including objects not even intended for this purpose. In actual practice, the objects most frequently used are screw drivers, polygonally shaped wrenches, and similar tools, whose hardness is invariably greater than that of the wall of the bore containing the mechanical override. Thus, depending on the type of object which is used, scoring of the wall of the bore may occur, and this can result in leakage through the end of the bore, an obviously undesirable result. While at first blush it might seem that this problem could be avoided by hardening the wall of the bore, it should be remembered that such hardening, apart from the extra cost involved, increases the magnetic permeability which is detrimental to the magnetic circuit.
Still another problem which may be present in a mechanical override is pulsing of the override when the valve spool is operated to a position which permits free movement of the override within its bore. Such pulsing may occur because of pressure differentials across the interior and exterior axial ends of the mechanical override giving rise to a net force acting on it. For example, if a full vacuum is drawn on the interior end of the override, a force equivalent to one atmosphere of pressure is applied as an inward force on the override. The present invention has the capability to resist pulsing of the override in response to the presence of such forces yet when intentional operation is desired, this resistive force can be readily overcome to permit the mechanical override to push interiorly of the valve.
The override cartridge of the present invention further has the attribute of being fabricated with well known conventional fabrication procedures.
Thus, the invention provides important benefits for the valve manufacturer, the machine manufacturer, and the end user.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be taken in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.